We investigate the performance of 25-Gbps dual-polarized orthogonal frequency division multiplexing (OFDM)-based modulation in a directly modulated distributed feedback (DFB)-laser over 25 km of single-mode fiber. A Volterra equalizer is used to compensate for the nonlinear effects of the optical fiber. The results show that FBMC-OQAM modulation outperforms OFDM, universal filtered multicarrier (UFMC), and generalized frequency division multiplexing (GFDM) waveforms. Indeed, a target bit error rate of ∼3.8 × 10 − 3 [forward error correction (FEC) limit] for FBMC, UFMC, OFDM, and GFDM can be achieved at −30.5, −26, −16, and −14.9 dBm, respectively. The effect of the DFB laser is also investigated for UFMC, OFDM, and GFDM, and they undergo a Q penalty of 2.44, 2.77, and 4.14 dB, respectively, at their FEC limit points. For FBMC-OQAM, the signal is perfectly recovered when excluding the DFB laser at −30.5 dBm.
Photonic crystal fibres (PCFs) with elliptical air-holes located in the core area that exhibit high birefringence, low losses,
enhanced effective mode area, and low chromatic dispersion across a wide wavelength range have been presented. The
effects of bending on birefringence, confinement losses and chromatic dispersion of the fundamental mode of the
proposed PCFs have been thoroughly investigated by employing the full vectorial finite element method (FEM).
Additionally, localization of higher order modes is presented. Also, effects of angular orientation on bending loss have
been reported. Significant improvement on key propagation characteristics of the proposed PCFs are demonstrated by
carefully altering the desired air hole diameters and their geometries and the hole-to-hole spacing.
In this paper we present a novel ultra-high-speed polymer electro-optic modulator that incorporates high permittivity
material cladding on the side walls of the device. We show that by packing the side walls of the modulator with this
material and varying the width of the dielectric stack and electrodes that broadband operation can be achieved whilst
maintaining a very low drive voltage in a compact device. The full-wave finite element analysis is employed in order to
determine any frequency dispersion effects with respect to the modulators half-wave voltage-length product,
characteristic impedance, microwave effective index and microwave dielectric losses.
Analysis and optimisation of ultra-high-speed Z-cut lithium niobate (LN) electrooptic modulator, operating at a high
frequency region, by using full wave finite element numerical technique has been demonstrated. Investigation of the
effects of adjusting the buffer layer thickness, the electrode height and the waveguide trapezoidal profile on the
microwave effective index (Nm), the characteristic impedance (Ζc), the microwave losses (αc) and the half-wave voltage-length
product (VπL) has been reported. Optimisation of the above parameters yield to a novel design of LN modulator
with a low VπL and high bandwidth operating at a frequency range between 1-100 GHz. The frequency dependent
dispersion of the key device parameters with aim to determine the device suitability for high speed operation has been
demonstrated.
Using a two-dimensional Finite-difference time-domain method (2D FDTD), we present an extensive study of a new
type of the wavelength multiplexer system. The self focusing and defocusing of the light beam are considered in this
paper. The coupling between different kinds of components integrated in the same chip, in terms of coupling efficiency,
is evaluated. Ultra-Dense Wavelength Division Multiplexing system (UDWDM) is of increasing demand since it
provides large broad spectra that satisfy large number of users
world-wide. This system can be used in the high-capacity
optical fibre communication systems. The UDWDM plays a central role in optical interconnection required for high-dense integrated systems, in terms of light coupling between various optical chips.
We report a novel type of dispersive structure for wavelength multiplexer/demultiplxer based on a 2D photonic
crystal (PC) prism. The novel device is proposed using super dispersion of a 2D PC. Simulation is carried out to
determine the angular dispersion as a function of the period. The design has been optimized to improve the
performance of a system with moderate refractive index contrast. It is shown that by varying the incident angle in a
wavelength range from 1.3μm to 1.5μm, a superprism effect is observed. The performance of the devices is
investigated in terms of sensitivity and resolution, which would help to understand the behaviour of the superprism
prior to fabrication and its integration in photonic circuits.
We have proposed a novel photonic crystal fibre (PCF), with three rings of air holes, that exhibit nearly zero ultra-flatted
and negative chromatic dispersion, and low confinement loss at a wide telecommunication window. Key PCF fabrication
parameters, such as the effects of air holes and their arrangements on the effective index, chromatic dispersion, effective
mode area, non-linear coefficient and confinement losses have been analysed by use of full vectorial finite element
method. Significant improvements of the PCF chromatic dispersion and confinement losses have been achieved when
supplementary air holes have been incorporated.
The effects of design parameters on the modulating voltage and optical bandwidth are reported for lithium niobate, GaAs and polymer electro-optic modulators by using rigorous numerical modelling techniques. It is shown that by etching lithium niobate, the switching voltage can be reduced and the bandwidth improved. For a GaAs-based modulator using higher aluminium content in the buffer layer, the device length can be shortened for a given optical loss. It is also observed that the dielectric loss and impedance matching play a key role in velocity-matched high-speed modulators with low conductor loss. It is also indicated in the work that by using tantalium pentoxide coating, velocity matching can be achieved for GaAs modulators. The effects of a non-vertical side wall on the polarisation conversion and single mode operation and the bending loss of polymer rib waveguide for electro-optical modulators are also reported.
Polarization conversion phenomenon in a semiconductor electrooptic polarization converter is reported by use of finite element method. The effects of various device parameters and the modulating voltage on the polarization of the TE and TM modes have been thoroughly investigated.
A numerical approach based on the two-dimensional (2D) Finite Difference Time Domain (FDTD) is employed to design, analyse and optimise the wavelength demultiplexer (WDM) based on photonic crystal waveguide couplers. The performance of the WDM is investigated in terms of device length, optical efficiency and losses. Significant improvement on the power efficiency and the wavelength directionality has been achieved by introducing a single defect on the crossing point between two photonic crystal waveguides.
The effects of design parameters on the modulating voltage and optical bandwidth are reported for lithium niobate, GaAs and polymer electro-optic modulators by using rigorous numerical techniques. It is shown that by etching lithium niobate, the switching voltage can be reduced and the bandwidth improved. For a GaAs-based modulator using higher aluminium content in the buffer layer for a given optical loss can shorten the device length. It is also observed that the dielectric loss and impedance matching play a key role in velocity-matched high-speed modulators with low conductor loss. It is also indicated in the work that by using tantalium pentoxide coating, velocity matching can be achieved for GaAs modulators. The effect of non-vertical side wall on the polarisation conversion and single mode operation and the bending loss of polymer rib waveguide for electro-optical modulators are also reported.
The effect of velocity matching, impedance matching, conductor loss and dielectric loss on the optical bandwidth is reported for Lithium Niobate and GaAs electro-optic modulators by using rigorous numerical techniques. It is shown that by etching Lithium Niobate the switching voltage and bandwidth can be improved and similarly by using a higher aluminium content in the buffer layer the device length for a given optical loss can be shortened. It is also observed that the dielectric loss and impedance matching play a key role in velocity matched high-speed modulators with low conductor loss. Finally it is indicated that by using tantalium pentoxide coating, velocity matching can be achieved for GaAs modulators.
The effect of velocity matching, impedance matching, conductor loss and dielectric loss on the optical bandwidth of an ultra-high-speed lithium niobate (LN) modulator is reported by using the finite element method. It is shown that for an etched LN modulator the product VπL could be reduced by 30% and it is also relatively easier to match both Nm and Zc simultaneously. The work indicates that both the dielectric loss and impedance matching play a key role for velocity matched high-speed modulators along with the low conductor loss. The effects of etch depth, buffer thickness, electrode width and the gap between the electrodes on device performance are also illustrated.
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